1. Field of the Invention
The present invention relates to a condensation preventing-apparatus for preventing a magnetic tape from sticking to a rotary drum due to condensation on the drum surface, which is caused by environmental change within storing or reproducing apparatus such as a rotary head type PCM magnetic storage and reproduction apparatus.
2. Description of Prior Art
A prior art rotary type PCM magnetic storage and reproduction (referred to R-DAT hereafter) such as video tape recorders (referred to as VTR), is an apparatus in which a signal is stored into and reproduced from a magnetic tape that is wrapped at an angle around a rotary drum on which a magnetic head is mounted.
With such prior art apparatus, water condensation is caused by environmental change such as the surface temperature of the rotary drum reaching the condensation point of the atmosphere, and therefore the magnetic tape sticks to the surface of the rotary drum causing soiling of the rotary drum and the head as well as damage to the magnetic tape.
Also, with a non-contact type apparatus using a disk, correct detection of a signal is impaired by the condensation on the head of a pickup.
FIG. 4 shows a prior art apparatus for overcoming the problem of water condensation. In FIG. 4, a condensation sensor 5 is mounted on a holder 12 in the vicinity of a fixed drum 1b.. When the condensation sensor 5 detects condensation, a drum-drying heater 9 on the fixed drum 1b is operated to dry up a rotary drum 1a and the fixed drum 1b. When the condensation sensor 5 detects vaporization of the condensed water, the drum drying heater 9 is stopped and then the magnetic tape (not shown) is loaded on t he rotary drum for storage and reproduction operation.
FIG. 5 is a block diagram for showing a prior art apparatus for preventing condensation in the R-DAT shown in FIG. 4. When electrical resistance of the condensation sensor 5 varies due to condensation a condensation detection circuit 6 outputs a condensation signal to a microcomputer 11. In turn, the microcomputer 11 actuates a heater drive circuit 10 to supply electric power to the drum drying heater 9. In this manner, the heat generated by the heater is conducted to rotary drum 1a through the fixed drum 1b, thereby heating up entire drum to dry the surface thereof.
In the meantime, the microcomputer 11 sends an operation command to a rotary drum drive circuit 4 and a tape loading mechanism drive circuit 3. These commands become ready as soon as the microcomputer is supplied with a signal from the condensation detecting circuit 6 indicating that the drum has been dried up. The tape loading mechanism 2 includes a guide pin for wrapping the magnetic tape around the drum and other mechanical parts (both not shown).
The shape and position of the holder for holding the condensation sensor 5 is selected for the sensor to effectively detect the drying condition and condensation condition of the rotary drum and the fixed drum.
FIG. 6 shows a flowchart for illustrating the operation of the microcomputer 11 used in the aforementioned prior art apparatus for preventing condensation. The apparatus is in a standby state at step S21 where the apparatus is switched on but has not been in the storing or reproducing state yet. When the condensation sensor 5 and the condensation detecting circuit 6 detect condensation at step S22, the heater drive circuit 10 is actuated to energize the drum-drying heater 9 at step 23.
Then microcomputer again makes a decision based on whether or not condensation has occurred at step S24. If condensation no longer exists, then the microcomputer proceeds to step S25 to shut off the drum-drying heater 9. The microcomputer permits the magnetic tape to wrap around the drum, i.e., tape loading operation at step S26, and then completes the series of the steps at S27. If the drum is not in a condensation condition and therefore no condensation signal is output at S22, then the microcomputer proceeds to step S26. If the drum is in a condensation condition at step S24, then the microcomputer returns to step S23 for causing the heater 9 to operate till the drum has dried up.
Condensation occurs frequently in automobiles in which environmental conditions can vary not only greatly but also frequently. Thus the above-mentioned prior art apparatus for preventing condensation condition, which operates only after condensation has occurred, cannot effectively reduce frequency of condensation.